An as-cast Ni-Al bronze (NAB) was subjected to friction-stir processing (FSP). The friction-stir processed NAB (FSPed NAB) exhibited better corrosion resistance in a 3.5 wt% sodium chloride solution. The corrosion product films formed on the as-cast and FSPed NAB were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and electron probe micro-analysis (EPMA). Uncorroded phases were retained in the films. The interfaces between these phases and their surrounding corrosion products allowed the chloride ions in and reduced the film protectiveness. For the as-cast NAB, the un-corroded phases were large in size or continuous in structure, resulting in continuous interfaces. Therefore, the film on the as-cast NAB exhibited relatively inferior protectiveness. The films on the as-cast and FSPed NAB were similar in composition with mainly copper chloride hydroxide Cu2(OH)3Cl in the outer layer, and Al2O3 and Cu2O with the incorporation of Fe and Ni in the inner layer. Stability of the films in the flowing condition was also studied and a film damage mechanism was raised. In the flowing condition, the film on the as-cast NAB was damaged by crack formation and expansion, while the film on the FSPed NAB was damaged by thinning.

An as-cast nickel aluminum bronze (NAB) was treated by friction-stir processing (FSP). Immersion test and electrochemical measurements under cavitation erosion condition were carried out to investigate the long-term and short-term corrosion behaviors of the as-cast and as-FSP NAB. Cavitation erosion tests were conducted in both distilled water and 3.5 wt% sodium chloride (NaCl) solution. The immersion test indicated that the electrochemical impedance of the as-FSP NAB was much higher, while there was little difference between them in the short-term test. The cumulative mass loss of the as-cast NAB was about 1.5 and 2 times as large as that of the as-FSP in distilled water and 3.5 wt% NaCl, respectively. The higher corrosion resistance of the as-FSP was a result of the refined and homogenized microstructure. Improved mechanical properties and fewer galvanic corrosion sites are attributed to the higher cavitation erosion resistance of the as-FSP NAB.